What's the point of having paralysis potions if everyone can resist them? Maybe its a mod I'm running, but it seems like every last bandit or mage etc can resist my potions - is there a potency that I'll get if I level up because it seems like there's only the time limit that is effected by your skill.

even the weak of body and mind can have a strong will.

Has to be a mod.
I use paralysis poison in tight spots, when surrounded and low on health and things go down quite statisfactory.
Mind that it does not work on dragons or undead including vampires, but for the rest, necromancers and Forsworn and the like go down fine.

If your making them yourself then I assume you need to keep putting perks into the tree to make them effective against higher level creatures. If that's the case then right now your fighting creatures that are higher than where you current alchemy skill is and should invest more perks into (I'm assuming).

As I understand it, paralysis poison is a flat effect without magnitude, like waterbreathing.
Perks and skill affect its duration, but not potency.

I've had it resisted before but I assumed it was just a small random chance that all NPC's have or something. It was only once though and not on anything that would normally resist it. Typically they drop like a rock which is especially funny if they are running towards you at the time it takes effect.